3 micron.Bryant FILCCFNC0024 and FILBBFNC0024 filterNominal size 20" x 23" x 4 1/4" (Actual size 19 7/8" x 22 5/8" x 4 1/4")Removes atmospheric and household dust, coal and insecticide dust, mites, pollen, tobacco smoke, cooking smoke, grease, mold, fungi and more down to 0..